1. Field of the Invention
This invention relates to a magnetic recording and reproducing apparatus which includes a plurality of printed wiring or circuit boards and whose electrical circuit is formed by connecting the printed wiring boards to each other by a cable.
2. Description of the Related Art
In a prior art magnetic recording and reproducing apparatus, its electrical circuit is divided into a plurality of sections formed on a plurality of printed wiring boards respectively, and these printed wiring boards are electrically connected to each other by a cable, so as to reduce the size of the housing of the apparatus or to prevent mutual interference by noise components generated from the electrical circuit of the apparatus. In such a prior art magnetic recording and reproducing apparatus, a signal conductor or line is electrically connected between the printed wiring boards for each kind of signals to be transmitted between these printed wiring boards.
FIG. 1 is a schematic block diagram showing the structure of an example of such a prior art magnetic recording and reproducing apparatus. For example, FIG. 1 shows the structure of a floppy disk drive having its electrical circuit formed by two printed wiring boards, that is, a printed wiring board for a motor circuit and a printed wiring board for record/reproduce control circuits.
In the floppy disk drive shown in FIG. 1, a disk cartridge 1 accommodating a magnetic recording medium 2 is loaded in the apparatus, and, in response to a demand from an externally connected system, information is recorded on or reproduced from the magnetic recording medium 2 by the function of magnetic heads 4 and 5. FIG. 2 is a schematic plan view showing the printed wiring boards and a connector between them in the floppy disk drive shown in FIG. 1.
Referring to FIGS. 1 and 2, the prior art magnetic recording and reproducing apparatus includes a spindle motor mechanism 3 for rotating the magnetic recording medium 2 accommodated in the disk cartridge 1, a head carriage 6 carrying magnetic heads 4 and 5 for recording information on the magnetic recording medium 2 or reproducing information from the magnetic recording medium 2, a step motor mechanism 7 for moving the head carriage 6 in a direction crossing the tracks on the magnetic recording medium 2, a record/reproduce control circuit board 8, a motor circuit board 9, and a cable 10 interconnecting the record/reproduce control circuit board 8 and the motor circuit board 9. Further, as shown in FIG. 2, the apparatus includes a disk cartridge detection switch 11 for whether or not the disk cartridge 1 is loaded in the apparatus, a write protect detection switch 12 for detecting whether or not the disk cartridge 1 is in its write protect state, an HD detection switch 13 for detecting whether or not the disk cartridge 1 is of the HD type, an ED detection switch 14 for detecting whether or not the disk cartridge 1 is of the ED type, an index sensor 15 for detecting the track reference position of the magnetic recording medium 2, and an LED 16 emitting light when the apparatus is in operation. In addition to those elements described above, the apparatus further includes a mechanism (not shown) for loading, holding and unloading the disk cartridge 1.
The record/reproduce control circuit board 8 is provided with a circuit 17 for driving the step motor mechanism 7, a recording and reproducing circuit 18 for recording a signal on the magnetic recording medium 2 or reproducing a signal from the magnetic recording medium 2 by means of the magnetic heads 4 and 5, a control circuit 19 for controlling the step motor drive circuit 17, the recording and reproducing circuit 18, the motor circuit board 9, etc., a connector 22 connecting the cable 10 for connection with the motor circuit board 9, and an interface connector 23 used for connection with a system (not shown) to which the apparatus is applied.
The motor circuit board 9 is provided with a spindle motor drive circuit 24 for driving the spindle motor 3, a spindle motor control circuit 25 for controlling the spindle motor drive circuit 24, a disk cartridge detection circuit 26 connected to the disk cartridge detection switch 11 for detecting whether or not the disk cartridge 1 is loaded in the apparatus, a write protect detection circuit 27 connected to the write protect detection switch 12 for detecting whether or not the disk cartridge 1 is in its write protect state, an HD detection circuit 28 connected to the HD detection switch 13 for detecting whether or not the disk cartridge 1 is of the HD type, an ED detection circuit 29 connected to the ED detection switch 14 for detecting whether or not the disk cartridge 1 is of the ED type, an index detection circuit 30 connected to the index sensor 15 for detecting whether or not the recording medium 2 is in its reference track position, an LED energization circuit 31 for energizing the LED 16 to signify that the apparatus is in operation, and a connector 34 connecting the cable 10 for connection with the record/reproduce control circuit board 8.
Three signals are usually supplied from the record/reproduce control circuit board 8 to the motor circuit board 9. That is, a signal MON is supplied to drive the spindle motor 3, a signal RPM is supplied to change over the rotation speed of the spindle motor 3, and a signal LED is supplied to energize the LED 16 to signify that the apparatus is in operation. On the other hand, five signals are usually supplied from the motor circuit board 9 to the record/reproduce control circuit board 8. That is, a signal IDX is supplied to index the track starting position, a signal DDP is supplied to indicate that the disk cartridge 1 is loaded or inserted already in the apparatus, a signal WPP is supplied to indicate that the disk cartridge 1 is in its write protect state, a signal HDP is supplied to indicate that the disk cartridge 1 is of the HD type, and a signal EDP is supplied to indicate that the disk cartridge 1 is of the ED type. In addition, at least two power supply conductors for connection with Vcc and GND are at least required for supplying power. Signal lines electrically connecting the printed wiring boards 8 and 9 to each other are prepared for all of these signals respectively. Therefore, in this case, a total of ten conductors (=eight signal lines plus two power supply conductors) are required to connect the printed wiring boards 8 and 9 to each other. These signal lines and power supply conductors are connected between the printed wiring boards 8 and 9 by soldering the cable 10 to the corresponding patterns provided on the wiring boards 8 and 9 or by means of the connectors 22 and 34, etc.
In the case of the prior art magnetic recording and reproducing apparatus described above, an increase in the number of the signals transmitted between the printed wiring boards 8 and 9 results in a corresponding increase in the number of the signal lines allocated to the individual signals respectively, and the area occupied by the cable 10 and the connectors 22 and 34 used for connection also increases. The increase in number of the terminals of the cable 10 and the connectors 22, 34 is disadvantageous in that the parts cost increases, and the reliability of the connection is lowered due to the increase in the soldered parts and the fitting parts between the connectors 22, 34 and the cable 10. On the other hand, the desired size reduction becomes difficult when the area occupied by the cable 10 and the connectors 22, 34 becomes wider. When an attempt is made to attain the desired size reduction without changing the number of the signal lines, the pitch between the terminals of the cable 10 and the connectors 22, 34 must inevitably be narrowed, resulting in lowering of the reliability of the connection.
In JP-U-63-151052, Kawada discloses that, when a plurality of printed wiring boards are connected by parallel buses, and a time-division multiplexing mode is used in a system of a small scale, the efficiency of communication in such a system can be improved. According to the above application, a bus protocol controller is provided for each of the printed wiring boards to be accessed so as to specify a peculiar bus protocol through an associated bus communication protocol line. Thus, according to the disclosure by Kawada, it is necessary to separately prepare the bus communication protocol lines, and the desired reduction of number of signal lines cannot be fully achieved.